1. Field of the Invention
This invention relates to magnetic cores formed from insulated microlamination particles and, more particularly, to such microlamination particles having a thin oxide coating on the surfaces.
2. Description of the Prior Art
Magnetic cores for power and high frequency uses are often produced from powdered metallic magnetic materials which comprise spheroids, flakes, and microlaminations. Flakes are usually made by flattening spheroid particles to a flake-like structure. Microlaminations are substantially flat, elongated, rectangular particles that are formed from plain carbon steel by cutting the same into discretely-shaped particles (elongated parallelopiped of generally rectangular cross-section) following which the microlaminations are decarburized, electrically insulated, and thereafter placed in a mold and pressed to the desired density without the use of a binder for producing the finished unitary magnetic core. Such powdered materials provide an economical method for production of magnetic cores which have low eddy current losses when subjected to high frequency excitation. Eddy current losses are reduced because of small particle size and high electrical insulation between the individual particles of the flakes. To obtain adequate core permeability, it is required that the insulation be sufficiently thin to provide a highly densified compact.
Heretofore, microlaminations have been provided with a coating of a suitable material, usually a magnesium oxide-based formation, for example, magnesium methylate, for providing electrical insulation between adjacent microlaminations in order to develop the required core loss characteristics in the finished product. U.S. Pat. Nos. 3,848,331 and 3,948,690 disclose the advantages and methods of applying such electrical insulation.
During a period of development of the use of insulated microlamination particles as material for magnetic cores, it had been the prevailing opinion that oxide coatings for insulating microlaminations from one another was not feasible because such oxides adversely affected the packing factor or density of the core produced from microlaminations. It was observed that the permeability exhibited by the core was adversely affected and became more severe as the frequency of the exciting current increased. Accordingly, it was a prevailing opinion that microlamination particles having oxide coatings were not suitably insulated from each other for use in magnetic cores and the like.